There is a well-established need for mesoporous oxide structures with tunable chemical activity for use as filters, reactors or sensors. One way to impart specific chemical functionality to such structures is to embed organic functionalities into the walls or onto the surfaces of the mesoporous oxides. These groups are either chemically active or can be further reacted to form chemically-active sites. Mesoporous ceramic structures with organic functionalities embedded in the walls and on the pore surfaces have been produced (Dag et al., “Oriented Periodic Mesoporous Organosilica (PMO) Film with Organic Functionality Inside the Channel Walls,” Adv. Funct. Mater. 11, 213-217 (2001); and Asefa et al., “Periodic mesoporous organosilicas with organic groups inside the channel walls,” Nature, 402, 867-871 (1999)). Commonly referred to as periodic mesoporous organosilicas (PMOs), these materials are generally formed as powders. Usually, aqueous based processing methods are used in their fabrication, although there are some references to alcohol-based processing methods which can produce such mesoporous films.
The primary limitation with the current above-described PMO methods is that the materials produced are structurally homogeneous. There is a need for multiple organic functionalities within a mesoporous structure and also for spatial separation of the mesoporous regions with these sites—needs that the above-described PMO methods do not currently meet.
Presently, organic groups can be incorporated into the walls of mesoporous silica in two ways. The first approach is a sequential process in which the mesoporous structure is formed, followed by deposition of a layer containing the desired organic groups. It is difficult to use this approach to produce regions with distinct organic groups because methods for selective deposition into targeted pore regions without simultaneous deposition onto other regions is considerably difficult. One method for accomplishing this was detailed in Doshi et al., “Optically Defined Multifunctional Patterning of Photosensitive Thin-Film Silica Mesophases,” Science, 290, 107-111 (2000), which describes the incorporation of a photoacid into a mesoporous structure and where ultraviolet (UV) light was used to selectively activate the structure in illuminated regions. However, this method cannot be universally applied because not all groups are responsive to photopatterning. The second approach is a single step process in which a precursor for the functional groups is incorporated into the precursor solution for the mesoporous oxide. Again, with this second approach, spatial control of the functional groups is lacking.
As a result of the foregoing, a more universal method of imparting differential chemical activity to pre-defined mesoporous regions within a structure so as to afford spatial control over the placement of such regions would be highly desirable.